Methods for selective modification of peptides are important for chemical biology and pharmaceutical industries. Among many reagents for modification, boronic acids have become a popular reaction partner for peptide under mild conditions. On the other hand, nitro aryl compounds have various roles in nature and industries. Its photosensitive properties lead to various photoreactions and applications as photo-labile protecting groups. This thesis has two main components: one component is about modification of peptides using boronic acids, and the other about the fate of nitro aryl moiety installed onto peptide using boronic acids. Chapter 1,4, and 5 belong to the first component. Chapter 1 is a review of peptide modification using boronic acids to form new C-C bond. Chapter 4 presents the development of a new method for peptide N-terminal modification using certain o-substituted boronic acids and copper (II) salts. The focus will be on method development for determining yield, and boronic acids scope screening. Chapter 5 will present an attempt of synthesizing peptide thioesters using histidine-directed peptide backbone arylation. Preliminary data with model peptides and potential future direction of the project will be discussed. Chapter 2 and 3 focus on nitro aryl compounds. Chapter 2 is a review about various photoreactions of nitro aryl compounds. Chapter 3 is a study of byproducts from photocleavage of nitroaromatic-containing peptide modification using small-molecule models. A bifurcating mechanism is proposed for reactions at different pH.